Chronic hyperglycaemia is a defining feature of diabetes mellitus, and consequent glucotoxicity most likely accounts for the associated microvascular disease, and contributes to premature macrovascular disease. Hence early and effective glycaemic control is fundamental to therapeutic intervention. There are two types of diabetes more prevalent viz. type 1 diabetes and type 2 diabetes. In type 1 diabetes, hyperglycaemia is due to complete or almost complete loss of insulin-secreting β cells from the pancreatic islets of Langerhans. In type 2 diabetes, however, hyperglycaemia indicates insulin resistance coupled with abnormalities of insulin production and secretion and other endocrinopathies that collectively cause a highly heterogeneous and progressive disorder. Treatment of type 2 diabetes is often complicated by coexistent obesity, which further impairs insulin action and aggravates hypertension, dyslipidemia, inflammation, and other pathogenic factors that promote cardiovascular risk. New types of glucose-lowering drugs are needed, preferably offering complementary and additional effectiveness to existing drugs, along with benefits against any of the common accompanying disorders such as obesity and cardiovascular disease.
Sodium-glucose cotransporters inhibitors (SGLTs), such as SGLT1 and SGLT2 inhibitors provide new therapeutic targets to reduce hyperglycaemia in patients with diabetes. SGLT1 enables the small intestine to absorb glucose and contributes to the reabsorption of glucose filtered by the kidney. SGLT2 is responsible for reabsorption of most of the glucose filtered by the kidney. Inhibitors with varying specificities for these transporters can slow the rate of intestinal glucose absorption and increase the renal elimination of glucose into the urine.
Currently various SGLT2 inhibitor drugs have been approved or in clinical phase for treatment of type 2 diabetes. A significant numbers of SGLT2 are β-C-arylglucosides derived drug candidates, most of which comprises a central 1-deoxyglucose ring moiety that is arylated at C1. Among β-C-arylglucosides the pharmaceutically valuable drugs that are now being marketed are Canagliflogin (Formula II), Dapagliflogin (Formula III), Empagliflogin (Formula IV), whereas Ipragliflogin (Formula V) is approved for marketing in Japan. The structures of these compounds are as given below:

There are various patents and patent applications viz., U.S. Pat. No. 6,515,117, U.S. Pat. No. 7,579,449, U.S. Pat. No. 7,772,407, U.S. Pat. No. 7,943,788, WO 2009035969, WO 2004063209, WO 2010022313, WO 2010043682, WO 2011047113, and WO 2013152476 which discloses the process for the preparation of these SGLT2 inhibitors. Most of these processes involve glucose or glucono lactone moiety for the preparation of the required compound.
In one of the prior art processes, hydroxyl group of the gluconolactone moiety is protected with trimethylsilane. The process discloses the reaction where after the C—C bond formation the resultant hemiketal formed is methylated using methanesulphonic acid. During the process the trimethylsilyl groups are hydrolysed and get removed. The demethylation of the methoxy group requires again protection with acetyl group followed by deacetylation to isolate the required compound that results in increased number of steps.
Another process discloses the protection of hydroxyl group of the gluconolactone moiety with acetyl group using controlled substance acetic anhydride. The protected gluconolactone is not available commercially and has to be prepared before the reaction.
Yet another process disclosed in the prior art, where the protection of hydroxyl group of the glucose moiety is carried out with pivaloyl chloride to get the compound pivaloyl-D-glucopyranose. Before the C—C bond formation, the pivaloyl-D-glucopyranose is reacted with bromine reagent to yield pivaloyl glucopyranosyl bromide compound which increases the number of steps and handling of bromine reagent.
The drawbacks of the above prior arts are:                1. The compounds glucose or gluconolactone when protected with pivaloyl, acetyl or trimethylsilyl groups need to be freshly prepared as the resultant compounds are unstable and not available on commercial scale.        2. The lack of stereoselectivity during formation of β-C-aryl glucoside reduces the yield of the product.        3. The process requires couple of protection and deprotection of the glucose moiety, which increases the number of steps and loss in yield of the final compound making the process uneconomical and cumbersome.        4. The glucose compound when protected with pivaloyl group requires the pivaloyl-D-glucopyranose compound to react with bromine reagent which increases the process cost and the number of steps and also involves the problem of handling of bromine reagent.        
In view of the above, there remains a need for stereoselective, more efficient and economic process for the preparation of β-C-arylglucosides. The present inventors ameliorates the prior art drawbacks by using the commercially available and stable Benzyl-D-glucopyranose moiety for the C—C bond formation reaction in the presence of strong alkali.